In the electronic materials field, there has been a trend in recent years toward making components lighter, thinner, and smaller, as well as toward using solder that is free of halogens, antimony, and lead, while at the same time even higher performance is being required of sealing materials and so forth.
Conventional semiconductor sealing resins, for instance, have been epoxy resin compositions obtained by curing a novolac epoxy resin with a phenol novolac resin.
However, as the high integration of semiconductors has increased, there has been a move toward lead-free solder in an effort to reduce package size and thickness and because of environmental concerns, and furthermore the requirements on sealing resins have been increasingly strict each year due to the development of pre-plated lead frames and so forth, which has made it difficult to ensure good reliability with conventional epoxy resin compositions. Specific characteristics that are required include adhesion to chips and lead frames, and in particular that there be no cracking, interfacial separation, or the like if [the resin composition] is immersed in solder after absorbing moisture.
In the field of paints, solvent-based paints are commonly used, but pollution restrictions targeting organic solvents have become stiffer and their enforcement is rapidly becoming a reality. In light of this situation, powder paints that contain no organic solvent whatsoever have been attracting attention. However, it is more difficult to obtain a thin film with these powder paints than with a solvent-based paint, and smoothness is also inferior. Along with these and other problems, polyester-based powder paints are said to have particularly low secondary adhesion to metals and the like.
The typical means for improving the adhesion of a resin to a metal or inorganic material is to add a silane coupling agent to the resin or subject the resin to a surface treatment with this agent.
With the above-mentioned sealing materials, epoxy-, amino-, and mercapto-based silane coupling agents are the most effective and have been in use for years, but with the above-mentioned environmental concerns and the move toward lighter, thinner, and smaller components in recent years, it is now increasingly common for the required characteristics to remain elusive. Also, since powder paints and the majority of sealing materials are in the form of powders, liquid silane coupling agents pose problems in terms of uniform mixing and ease of handling. There has been a need for a solid silane coupling agent that would meet these requirements, but none is commercially available at this time, so liquid silane coupling agents still have to be used.
It has already been proposed that a silane coupling agent be mixed and reacted with a phenol resin, and the resulting reaction product be used as the epoxy resin composition component in sealing material applications (Patent Documents 1 to 6) . Since the silane coupling agent is in liquid form, this reaction product can be pulverized in solid form if the ratio of silane coupling agent/phenol resin is low, but as the proportion of silane coupling agent increases, the reaction product gradually becomes softer (its softening point decreases) and it can no longer be pulverized. Although it varies with the silane coupling agent, a silane coupling agent containing one or more functional groups from among a vinyl group, glycidyl group, styryl group, methacryl group, acryl group, ureido group, chloro alkyl group, mercapto group, and isocyanate group cannot be pulverized unless contained in an amount of just a few percent to no more than 10% (with the remainder being phenol resin).
A method in which an alcohol is removed after the mixing of silane coupling agents is discussed in Patent Documents 2 to 5. The softening point rises when an alcohol is removed, but a condensation reaction between the silane coupling agents produces siloxane bonds and gelling, so the anticipated increase in adhesive strength is not always achieved. Meanwhile, with a basic silane coupling agent containing one or more functional groups from among an amino group, dimethylamino group, and imidazole group, the amino, dimethylamino, or imidazole groups become a catalyst in the hydrolysis of the alkoxysilyl groups in the silane coupling agent, which tends to accelerate the reaction of the phenol with hydroxyl groups and the condensation reaction between the silane coupling agents, so the product tends to be a solid. Nevertheless, because these basic silane coupling agents have such strong catalytic activity, they do increase adhesive strength when added to a sealing material, but they also lower fluidity, which makes problems more apt to occur in transfer molding.
A method involving a reaction (mixing) between a phenol resin and a silane coupling agent is discussed in Patent Documents 2 to 5. All of these patents involve mixing a silane coupling agent with a phenol resin at high temperature, and removing the alcohol that is produced. Here, as mentioned above, solidification occurs with no problem if the silane coupling agent content is only a few percent (with the rest being phenol resin), but the action of the silane coupling agent as a phenol resin curing agent is too strong, so the resulting reaction product is more accurately called a phenol resin modified with a silane agent rather than a solid silane coupling agent, with substantially all of the alkoxysilane groups (SiOR groups) being consumed. As a result, an adequate coupling effect is not obtained, and the increase in adhesion is still inadequate. Also, since a phenol resin acts as a curing agent on epoxy resins, when one is added to an epoxy resin composition, it upsets the epoxy resin/curing agent ratio. When a phenol resin is the curing agent, the amount of phenol resin added should be controlled, but with other curing agents problems with characteristics are sometimes encountered. Accordingly, the silane coupling agent content in a solid coupling agent should be as high as possible.
On the other hand, if the silane coupling agent content is raised, condensation between the silanes is less likely to occur in the removal of the alcohol produced by the reaction between the silane coupling agent and the phenol resin, and the gelling that occurs prevents dissolution in the solvent. This gelled reaction product is difficult to mix with the resin when a resin composition is heated and melted and subjected to a curing reaction, the coupling effect of the silane coupling agent is inadequate, and the desired increase in adhesion is not realized.
Because of this, it is stated in paragraph 0032 of Patent Document 4 that the proportion of a silane coupling agent to a phenol resin is 0.1 to 50 wt %, and preferably 1 to 30 wt %, but because of the need for solidification, the amount is given as 10 wt % or less in the actual examples. In the examples given in Patent Documents 2, 3, and 5, the silane coupling agent content is also given as 10 wt % or less.
Patent Document 1: Japanese Patent Publication 7-17739B    Patent Document 2: Japanese Patent No. 2,506,220    Patent Document 3: Japanese Patent Publication 7-94534B    Patent Document 4: Japanese Patent Publication 9-67427A    Patent Document 5: Japanese Patent Publication 2002-128867A    Patent Document 6: Japanese Patent Publication 59-181036A